1) Field of the Invention
This invention generally relates to high-temperature sterilization of electronic devices and electromechanical devices and, more particularly, to systems to protect electronic components against the damaging effects of high-temperature sterilization.
2) Discussion of Related Art
Excess thermal energy (i.e., heat) is generally considered undesirable and harmful to electronic circuits. Electronic components of consumer and military electronic devices are each designed to operate within a specific temperature range, depending on the anticipated operational environment and the expected service parameters of the particular component. Generally, the higher the temperature that a particular electronic device or component can withstand without operational failure (or shortened lifespan), the more expensive that component will be to manufacture. Any device which requires many of such high-temperature-rated components, will, of course, end up being expensive as well.
Essentially, all electronic components generate some heat by dissipating energy as they operate. To this end, effective thermal management is important so that the upper end of the operational temperature range may be increased without the component failing. Most semiconductor devices, for example, are not rated for junction temperatures above 175° C., and their performance degrades rapidly with increased temperatures exceeding that upper limit, especially if the applied high temperature is maintained for relatively long periods of time. Interestingly, electronic components that are operating under power are substantially more sensitive to thermal damage than the same components isolated from a power source.
It is common to design thermal management structures and systems into a circuit to help prevent thermal-related failure of the operating components. Most thermal management includes mechanical heat-conduction structure designed to draw heat energy away from the electronic devices, as the heat is generated within or adjacent the component. Such structure includes heat sinks, cooling fans, and liquid-cooling systems, etc.
These cooling systems generally work well at removing excess heat from an operating electronic device because in most cases, there is access to a cooler region into which the excess energy generated by the particular electronic component may easily and naturally migrate, resulting in a cooler operating component. Unfortunately, certain electronic devices are forced to operate in a super-heated environment for a prolonged period of time (between 2 and 120 minutes depending on the sterilization temperature, device size, mass and complexity) where, by the very nature of the environment, no such temperature gradient can effectively exist.
A variety of mechanical and electro-mechanical devices must operate in environments that require the devices to be completely isolated within a protective barrier. In some situations, the “outside environment” (environment located outside the barrier) is hazardous and includes elements or conditions that will adversely affect the operation of the device or shorten its expected useful operative life. In such hazardous environments, the device must be completely sealed and the protective barrier must be made with the particular hazard in mind. For example, implanted devices must be hermetically sealed to prevent the penetration of moisture, which would adversely affect the operation of the device. Also, many medical devices that are to be implanted within a human patient, for example, must also be hermetically sealed, primarily, in this delicate living environment, to prevent infection or contamination caused from within the device.
Certain biologically implanted devices include delicate electronic components typically including integrated circuits, memory chips, and solid state sensors, that are powered by on-board, hermetically-sealed batteries and are all sensitive to high temperatures. Pace-makers, defibrillators, stimulators, drug-delivery devices (such as infusion pumps) are some examples of such powered, implanted devices wherein, for biological-safety reasons, the electronic components and the power supply are both permanently sealed within a metal housing and owing to the sealed arrangement requirements, cannot be mechanically or electrically accessed from outside the housing. The batteries used are built into the device and will provide the necessary power for the operational life of the device.
After manufacture of such devices and prior to them being used (or surgically implanted within a patient), the entire device must be sterilized using either a gas-sterilization system, a gamma radiation system or steam. If a gas is used, typically, Ethylene Oxide (ETO) is applied to the device for a controlled period of time. Sterilizing using ETO may be effective, but many materials tend to absorb the ETO chemical during the process. These components must be properly aerated after the ETO gas has been applied. Furthermore, in such applications wherein the sterilized device contacts humans, new studies have shown that an increasing number of people are sensitive to even the trace amounts of ETO residing on the device after ETO sterilization is complete.
Gamma radiation or E-beam application may be applied to the device to effectively sterilize the entire device, but unfortunately, such radiation applications have been shown to degrade or otherwise damage certain plastic and rubber compounds and, sadly, also electronic components.
Steam sterilization is a simple and effective process and is generally preferred over using ETO or gamma radiation. However, since the system uses heat to kill any microbes on the device, the required temperatures can likely damage onboard electronic components and onboard batteries.
To ensure thorough sterilization, super-heated steam is applied to the hermetically-sealed electronic device for a period generally between 2 and 120 minutes (depending on the sterilization temperature, device size, mass and complexity), during which time the entire device, including any on-board circuitry and batteries will become super-heated. During the sterilization process, all of the components of the device will eventually reach a temperature between 120 and 135 degrees Celsius. Electronic circuits operating in this super-heated environment (while electrically connected to the on-board batteries) for such a prolonged period of time will invariably suffer irreparable thermal damage and will likely fail either immediately, or sometime before its expected operational life has been reached. This potential for failure is incredibly undesirable considering that the device will eventually operate long-term within a human and will likely help the human to live.
Of course, some of the heat-related damage caused by the steam-sterilization process can be mitigated by using high-specification components (e.g., military-spec components). These components undergo critical testing during their manufacture and have been otherwise designed to handle higher temperatures. The problems associated with these military grade components include size, availability, and cost. The military grade components are generally larger and more expensive than their equivalent commercial-grade components. Furthermore, not all components are available in military grade. Considering typical commercial viability of the end product and the limited space available, use of such expensive and larger military-spec components is generally difficult to justify, leaving little option but to rely on cheaper, smaller, yet more-heat sensitive components for many of the devices that must be sterilized.
It is therefore an object of the present invention to provide a thermal-related protection to electronic components, which overcomes the deficiencies of the prior art.